Systems and methods for reducing interference in CDMA systems

• US 20040146093A1
• Filed: 10/31/2003
• Published: 07/29/2004
• Est. Priority Date: 10/31/2002
• Status: Abandoned Application

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Narayan, Anand P., Olson, Eric S.
• Application Number:
  US10/699,360
• Publication Number:
  US 20040146093A1
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 1/71052 using decorrelation matrix
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers

Abstract

The systems and methods described herein provide a processing engine useful in a communications receiver. The processing engine substantially reduces interference caused by unwanted signals by mathematically reducing the energy of the signals. In one embodiment, the signals have known CDMA coding schemes. The signals are selectively substantially cancelled using a matrix generated, at least in part, from determined CDMA codes. For example, a receiver of one embodiment includes a demodulator unit for determining a code from each of a plurality of signals and for demodulating one or more of the plurality of signals. The processing engine is communicatively coupled to the demodulator unit and configured for generating a matrix of one or more vectors based on determined codes. Each element of the vectors comprises a component of the determined codes and the matrix itself is used to selectively substantially reduce energy from one or more of the signals.

Claims

1. A receiver, comprising:

a demodulator unit configured for determining a code from each of a plurality of signals and for demodulating one or more of the plurality of signals; and

a processing engine communicatively coupled to the demodulator unit and configured for generating a matrix of one or more vectors based on determined codes, wherein each element of the vectors comprises a component of the determined codes and wherein the matrix is used to selectively substantially reduce energy from one or more of the signals.

2. The receiver of claim 1, further comprising a searcher finger configured for selecting signals for demodulation from said plurality of signals and for determining one or more codes from selected signals.

3. The receiver of claim 2, wherein the demodulator unit comprises a plurality of demodulator fingers configured for demodulating the selected signals.

4. The receiver of claim 2, wherein the determined codes comprise code offsets in time from one another.

5. The receiver of claim 1, wherein the matrix comprises one composite interference vector having one or more elements, wherein each element of the vector includes a component of a determined code and a relative amplitude of one of the signals associated with the determined code.

6. The receiver of claim 1, wherein each vector of the matrix has one or more elements, each element comprising a component of a determined code associated with one of the plurality of signals.

7. The receiver of claim 1, wherein the receiver further comprises a radio frequency front end configured for receiving the signals.

8. The receiver of claim 7, wherein the processing engine comprises a channel selector configured for selecting components of the determined codes from signals selected for energy reduction.

9. The receiver of claim 8, wherein the processing engine is further configured to generate a cancellation operator used to substantially reduce the energy of the signals selected for energy reduction.

10. The receiver of claim 9, wherein the cancellation operator comprises a projection operator P_s^⊥

having the following form;

P_s^⊥

=I−

S(S^TS)<sup>−

1</sup>S^T,

where I is an identity/matrix, S is the matrix and S^T is a transpose of the matrix.

11. The receiver of claim 10, wherein the processing engine comprises an application unit configured for applying the projection operator P_s^⊥

to a desired code x to selectively substantially reduce one or more of the plurality of signals, wherein the projection operator P_s^⊥

is applied to the desired code according to the following form;

P_s^⊥

x=(I−

S(S^TS)<sup>−

1</sup>S^T)x.

12. The receiver of claim 1, wherein the determined codes are selected from a group consisting of a spreading code and a covering code.

13. The receiver of claim 12, wherein the spreading code is a short code.

14. The receiver of claim 12, wherein the covering code is selected from a group consisting of a Walsh code and a quasi orthogonal function code.

15. The receiver of claim 1, wherein the signals are selected from a group consisting of cdma2000 signals and cdmaOne signals.

16. A method for reducing interference to a desired signal, comprising:

determining a code from each of a plurality of signals;

generating a matrix of one or more vectors based on determined codes, wherein each element of the vectors comprises a component of the determined codes; and

using the matrix to selectively substantially reduce energy from one or more of the signals thereby reducing interference.

17. The method of claim 16, further comprising demodulating one or more signals from said plurality of signals.

18. The method of claim 16, further comprising determining one or more codes of signals selected said plurality of signals.

19. The method of claim 16, wherein generating comprises constructing the matrix from one composite interference vector having one or more elements, wherein each element of the vector includes a component of a determined code and a relative amplitude of one of the signals associated with the determined code.

20. The method of claim 16, wherein generating comprises constructing the matrix from a plurality of said vectors, wherein each vector of the matrix has one or more elements, each element comprising a component of a determined code associated with one of the plurality of signals.

21. The method of claim 16, wherein using the matrix comprises generating a cancellation operator for application to a desired code to substantially reduce the energy of the signals selected for energy reduction.

22. The method of claim 21, wherein generating the cancellation operator comprises generating a projection operator P_s^⊥

having the following form;

P_s^⊥

=I−

S(S^TS)<sup>−

1</sup>S^T,

where I is an identity matrix, S is the matrix and S^T is a transpose of the matrix.

23. The method of claim 22, further comprising applying the projection operator P_s^⊥

to the desired code to selectively substantially reduce one or more of the plurality of signals, wherein the projection operator P_s^⊥

is applied to the desired code according to the following form;

P_s^⊥

x=(I−

S(S^TS)<sup>−

1</sup>S^T)x,

where x is the desired code.

24. A system for reducing interference to a desired signal, comprising:

means for determining a code from each of a plurality of signals;

means for generating a matrix of one or more vectors based on determined codes, wherein each element of the vectors comprises a component of the determined codes; and

means for using the matrix to selectively substantially reduce energy from one or more of the signals thereby reducing interference.

25. The system of claim 24, further comprising means for demodulating one or more signals from said plurality of signals.

26. The system of claim 24, further comprising means for determining one or more codes of signals selected from said plurality of signals.

27. The system of claim 24, wherein the means for generating comprises means for constructing the matrix from one composite interference vector having one or more elements, wherein each element of the vector includes a component of a determined code and a relative amplitude of one of the signals associated with the determined code.

28. The system of claim 24, wherein the means for generating comprises means for constructing the matrix from a plurality of said vectors, wherein each vector of the matrix has one or more elements, each element comprising a component of a determined code associated with one of the plurality of signals.

29. The system of claim 24, wherein the means for using the matrix comprises means for generating a cancellation operator for application to a desired code to substantially reduce the energy of the signals selected for energy reduction.

30. The system of claim 29, wherein the means for generating the cancellation operator comprises means for generating a projection operator P_s^⊥

having the following form;

P_s^⊥

=I−

S(S^TS)<sup>−

1</sup>S^T,

where I is an identity matrix, S is the matrix and S^T is a transpose of the matrix.

31. The system of claim 30, further comprising means for applying the projection operator P_s^⊥

to the desired code to selectively substantially reduce one or more of the plurality of signals, wherein the projection operator P_s^⊥

is applied to the desired code according to the following form;

P_s^⊥

x=(I−

S(S^TS)<sup>−

1</sup>S^T)x,

where x is the desired code.

32. A processing engine, comprising:

a matrix generator configured for generating a matrix having one or more vectors, wherein the matrix is generated based on a plurality of codes and wherein each element of the vectors comprises a component of the codes; and

an application unit communicatively coupled to the matrix generator and configured for using the matrix to selectively substantially cancel one or more of a plurality of signals.